We carried out a double blind control study of fatigue in 32 patients with multiple sclerosis, comparing amantadine hydrochloride 100 mg twice a day and placebo. On amantadine 31% had marked improvement; 15.6% moderate improvement; 15.6% mild improvement; and 36.5% unchanged. On placebo, none noted marked improvement; one claimed moderate improvement on either amantadine or placebo. 18.7% reported mild improvement on placebo; and most of them had similar or more response to amantadine. No patient selected placebo over amantadine at the end of the trial. Overall improvement was seen in 62.5% of patients on amantadine and 21.8% on placebo. Additional experience up to two years suggests continued benefit but common and important side-effects.